San Antonio Mayor Julian Castro (l.), who will be the convention keynote speaker, and his twin brother, State Representative Joaquin Castro, who is running for U.S. Congress, are interviewed at the Democratic National Convention in Charlotte, N.C., Monday.

Charlotte, N.C. — Who is Julian Castro? He’s the mayor of San Antonio, Texas, and tonight’s keynote speaker at the Democratic National Convention, that’s who.

He’ll be the first Hispanic to ever deliver the DNC keynote. Democrats think he’s popular enough to rise to Lone Star State governor, or even higher office. He’s got a compelling personal story – he was raised by a strong single mom who was herself politically active. He’s got an identical twin brother who represents San Antonio in the state legislature and is likely to be elected to Congress in November.

He’s young, only 37, and has risen fast. Sound like anyone else? Yes, that’s what we thought too – he’s the Democrats' answer to Sen. Marco Rubio of Florida. Except Senator Rubio’s not an identical twin.

Rubio did well for himself in Tampa, Fla., with a speech that some political analysts think may have set him apart from New Jersey Gov. Chris Christie, vice presidential nominee Paul Ryan, and other non-Romney party heavyweights. Mr. Castro’s not at Rubio’s level yet in the sense that nobody’s talking about him as a potential 2016 nominee. But in giving the San Antonio mayor the keynote speech, Democrats may be trying to broaden their bench of nationally known figures, while attempting to woo the Hispanic vote. A twofer.

Castro's father and mother split up when he was eight. He and twin sibling Joaquin were raised by their mom, Maria “Rosie” Castro, who was an organizer in the Texas Mexican-American community in the 1970s. Her activities drew hate mail and even the interest of the Justice Department.

But today Castro says it was his mom and others like her who broke barriers, allowing Hispanics like him to have a political future.

“It was very warranted at that time,” he told the Associated Press. “You had a huge dropout rate. You had signs that said, ‘No Mexicans or dogs allowed.’ It was a movement born out of both aspiration and frustration, it was very understandable. And ultimately, I believe, [it] helped move this country forward.”

His mom emphasized grades as well, paying for high marks. That paid off – Castro went to Stanford and Harvard Law. He’s the youngest person ever elected to the San Antonio City Council, where he won a seat in 2001. He lost a try for the mayor’s seat in 2005, then came back to win on his second try, in 2009. He was reelected in 2011.

He’s a nonpartisan office holder in a city manager form of government, notes the Dallas Morning News today in a good piece on his background. Castro “brings a life of contrasts” into his keynote address, writes the Dallas paper’s Robert T. Garrett. He’s a shy politician, a red state Democrat, and so on.

“Castro is hyped as a future statewide or even national candidate despite his short resume. The mayor, though, has dug in to solve problems at the local level for most of a decade – and plans to stay there for a while,” writes Mr. Garrett.

Republicans, though, say that they’ve seen this movie before – in 2004, when the young and unknown Barack Obama got the chance to boost his national profile by delivering a DNC keynote.

Conservatives criticize the choice of Castro by saying he’s done little to actually merit an appearance hundreds of more experienced politicians would love to make.

“It is kind of creepy to see just how many hurrahs and hosannas a politician [can] generate without actually doing much of anything, particularly on bread-and-butter issues like crime and education. If a Castro defender wants to argue he’s only been in office three years, fine ... but that just raises the question of why an unaccomplished mayor is giving the keynote address. It’s like watching the Obama playbook from 2004 all over again,” writes the National Review’s Jim Geraghty in his The Campaign Spot blog.